7. Formulations for the GIT Flashcards
Oral liquids
- Lactulose (laxative)
- Pedialyte (ORT)
- Omeprazole suspension (PPI)
- Mylanta liquid (antacid)
Oral powders
- Enerlyte (ORT)
- Movicol (laxative)
- Psyllium (laxative)
Oral disintegrating tablet/effervescent tablets
- Ondansetron (anti-emetic)
- Gastrolyte (ORT)
Oral liquid dosage forms
Allow:
- Rapid onset of action (ready for absorption/have local effect)
- Ease of swallowing (paediatrics or nausea/vomiting)
- Flexible dosing
Are limited by:
- Reduced stability
- Bulky nature
- Pronounced taste
- Dosing variability (patient error)
Mitigating oral liquid drawbacks
Stability can be enhanced by:
- Incorporating excipients
+ E.g. Preservatives (microbial protection), antioxidants
- Storage conditions
+ Refrigeration slows degradation (Arrhenius equation)
- Using rapidly dissolving tablets or powders
+ Stable in solid form, can be administered in liquid form
+ Also eliminate concerns of “bulky nature” & “dose variability” (tablets & powder sachets have defined dose)
- Taste can be enhanced by
+ Flavours & sweeteners
Why are antacid tablets chewable?
MoA – contain alkaline salts that neutralise stomach acid
Need to act fast
- Gastric emptying offers short timeframe
- Larger surface area = faster chemical reaction
Chewable tablets give
+ Solid dosage form advantages (defined dose, high stability, convenient to carry)
+ Chewability increases surface area for quicker reaction
- Easier to swallow
Liquid antacids are also available
Raft forming alginates - how they work
E.g. Gaviscon contains
- Sodium alginate
- Potassium bicarbonate
- Calcium carbonate
- In acid the alginate precipitates, forming a gel
- Calcium ions help cross link & strengthen the alginate gel
- Bicarbonate reacts with acidic contents to form CO2
Enteric coats
- GI tract has variable pH
- Polymers are available that demonstrate selective solubility at different pH
Why do we use enteric coatings?
Peppermint oil
- Oil degrades in stomach
- Causes GI symptoms
- Loss of efficacy
Omeprazole
- Degrades rapidly in acidic conditions
Mesalazine
- Degrades rapidly in acidic conditions
- Sometimes needed to target specific parts of GI tract
+ Asacol -> enteric coating designed to dissolve only at pH > 7 (targets terminal ileum & colon)
Aspirin
- Causes gastric ulceration
Novel enteric coating - Phloral
Dual functioning enteric coating containing
- pH sensitive polymer (Eudragit S)
- Polysaccharide (resistant starch)
When it reaches the colon, it will
- Break down due to the high pH
AND/OR
Break down due to digestion by microorganisms
Pill burden = Formulation issue?
- Patient compliance is key to formulation effectiveness
- Selected dosage regimens all boil down to formulation design
H. pylori infection
- Triple or quadruple therapy required for 7 days
- 6 or more tablets/capsules per day
- Losec HP7 or Nexium HP7 available elsewhere
+ No combined packaging available in NZ
Powders for reconstitution
Omeprazole has poor stability in liquids
+ Rapidly hydrolysed, particularly in acidic conditions
Injectable omeprazole is available as a “powder for injection”
- Ensures high stability
- Dilute/reconstitute immediately before injection
Injectable omeprazole 40 mg
Available as “injection” or ”infusion”
Omeprazole injection:
- Reconstitute in 10 mL diluent containing macrogol 400 & citric acid monohydrate (provided in pack)
- Slowly injected over 2.5 minutes
Omeprazole infusion:
- Dilute in 100 mL dextrose 5% or 100 mL saline
- Stable for 6 h in dextrose & 12 h in saline
What about omeprazole suspension?
Prepared in sodium bicarbonate solution
- pH 8.4
- Slows down hydrolysis
Store at 2 – 8 degrees
- Slows down hydrolysis
Stable for 14 days
Suppositories
To be administered rectally
Suppositories regularly used for systemic effects
- Paediatrics
- Nil by mouth
- Seizures
May use for local effects
- Only use for rectal area, or slightly higher
+ Proctitis/eczema
+ Haemorrhoids (ointments also usually available)
+ Constipation (glycerol, Bisacodyl)
